Greater efficacy of a combination of conservative therapies for thumb base OA in individuals with lower radial subluxation - a pre-planned subgroup analysis of the COMBO trial.

OBJECTIVE: To investigate heterogeneous effects of a combination of conservative therapies compared with an education comparator for thumb base (TB) osteoarthritis (OA) according to clinically relevant characteristics. METHODS: Pre-planned subgroup analysis of the COMBO trial (n = 204) which compared a combination of education on self-management and ergonomic principles, a prefabricated neoprene splint, hand exercises, and diclofenac sodium gel, with education alone for radiographic and symptomatic TB OA. Primary outcomes were change in pain (visual analogue scale [VAS], 0-100 mm) and hand function (Functional Index for Hand Osteoarthritis questionnaire, 0-30) from baseline to week-6. Other outcomes were grip and tip-pinch strength and patient's global assessment (PGA) (VAS, 0-100 mm). Possible treatment effect modifiers were the presence of interphalangeal joint pain, erosive hand OA, radiographic thumb carpometacarpal joint subluxation (higher vs equal or lower than the sample mean), and baseline radiographic OA severity (Kellgren Lawrence grade). Linear regression models were fitted, adding interaction terms for each subgroup of interest. RESULTS: The treatment effects of the combined intervention at 6 weeks were greater in participants with lower joint subluxation compared with those with greater subluxation (pain -11.6 [95%CI -22.2, -9.9] and 2.6 [-5.5, 10.7], respectively, difference between the subluxation groups 14.2 units (95% CI 2.3, 26.1), p-value 0.02; and PGA -14.0 [-22.4, -5.5] and 1.5 [-6.2, 9.3), respectively, difference between the subluxation groups 15.5 units (95% CI 4.2, 26.8), p-value 0.03). There was no statistically significant heterogeneity for the other subgroups. CONCLUSION: A combination of conservative therapies may provide greater benefits over 6 weeks in individuals with lower joint subluxation, although the clinical relevance is uncertain given the wide confidence intervals. Treatment strategies may need to be customized for those with greater joint subluxation. TRIAL REGISTRATION NUMBER: ACTRN 12616000353493.

Radial subluxation in relation to hand strength and radiographic severity in trapeziometacarpal osteoarthritis.

OBJECTIVE: Greater joint laxity and radial subluxation of the thumb metacarpal base have been shown to be risk factors for the development of trapeziometacarpal osteoarthritis in an asymptomatic and radiographically normal joint. Despite this, it is unknown whether joint laxity changes with disease progression from mild to severe osteoarthritis. This study aimed to investigate the relationship between joint laxity and osteoarthritis severity, using the trapeziometacarpal subluxation ratio as an indicator of joint laxity. METHOD: Baseline data were used from the first 100 participants included in the COMBO (Efficacy of combined conservative therapies on clinical outcomes in base of thumb OA) trial. All participants had bilateral posteroanterior (PA) and Eaton stress view hand radiographs, as well as grip and tip-pinch strength measurements. The PA view was used to assess Kellgren-Lawrence and Eaton grades, and the Eaton stress view was used to assess the trapeziometacarpal joint subluxation ratios. Generalised estimating equations were utilized to account for the fact that hand data are paired, and within-person measurements are therefore not independent. RESULTS: Lower radial subluxation ratios were associated with higher Kellgren-Lawrence grades (B-coefficient -0.302; p-value 0.027), and lower grip strength scores (B-coefficient 2.06; p-value 0.006). CONCLUSIONS: Radial subluxation ratios decreased with increasing disease severity, contrary to the progression from a normal joint to one with mild osteoarthritis, wherein higher joint laxity is a risk factor for disease. This may be explained by the mechanical stabilization provided by osteophytes and capsular changes in worsening osteoarthritis, as has been shown to be the case in the knee. TRIAL REGISTRATION NUMBER: ACTRN 12616000353493. LEVEL OF EVIDENCE: III.